Apparatus and method for minimally invasive total joint replacement

ABSTRACT

A method and apparatus for minimally invasive total joint replacement. The method involves sculpting the articular surface of a second bone that normally articulates with a first bone by attaching a bone sculpting tool directly or indirectly to the first bone with the tool in bone sculpting engagement with the articular surface of the second bone, and then sculpting the articular surface of the second bone with the joint reduced and moving one bone with respect to the other. An implant is placed to replace the articular surface of the second bone using an impaction device directly or indirectly attached to the first bone, wherein the force to place the implant is reacted by the second bone and the first bone.

This application is a continuation in part of Ser. No. 09/882,591, filedJun. 18, 2001 and claims benafit of Provisional Appr. No. 60/331,930filed Nov. 21, 2001.

BACKGROUND OF THE INVENTION

A joint generally consists of two relatively rigid bony structures thatmaintain a relationship with each other. Soft tissue structures spanningthe bony structures hold the bony structures together and aid indefining the motion of one bony structure relative to the other. In theknee, for example, the bony structures are the tibia and the femur. Softtissue such as ligaments, tendons, menisci, and capsule provide supportto the tibia and femur. A smooth and resilient surface consisting ofarticular cartilage covers the bony structures. The articular surfacesof the bony structures work in concert with the soft tissue structuresto form a mechanism that defines the envelop of motion between thestructures. When fully articulated, the motion defines a total envelopof motion between the bony structures. Within a typical envelop ofmotion, the bony structures move in a predetermined pattern with respectto one another. In the example of the hip joint, the joint is a ball insocket joint that is inherently stable. The capsule and ligamentsspanning the hip joint provide stability while the muscles providemotion.

The articular surfaces of the bony structure became damaged by a varietyof diseases, accidents, and other causes. A common disorder of joints isdegenerative arthritis. Degenerative arthritis causes progressive pain,swelling, and stiffness of the joints. As the arthritis progresses thejoint surfaces wear away, resulting in contractures of the surroundingsoft tissues that provide stability to the joint. Moreover, progressionof the disease process increases pain and reduces mobility.

Treatment of the afflicted articular bone surfaces depends, among otherthings, upon the severity of the damage to the articular surface and theage and general physical robustness of the patient. Commonly, foradvanced arthritis, joint replacement surgery is necessary wherein thearticulating elements of the joint are replaced with artificial elementscommonly consisting of a part made of metal articulating with a partmade of ultra high molecular weight polyethylene (UHMWPE).

A relatively young patient with moderate to severe degeneration of thehip joint is often treated with drug therapies. While drug therapies maytemporarily provide relief of pain, progression of the disease, withresulting deformity and reduced function, ultimately necessitatessurgery. Alternative treatments such as non-steroidal anti-inflammatorydrugs and cortisone injections similarly provide only temporary reliefof symptoms.

In severe situations, the entire articular surface of a bone may bereplaced with an artificial surface, as, for example, when theacetabular socket and femoral head are replaced with a prosthetic deviceincluding an UHMWPE bearing to resurface the acetabulum and a polishedmetal or ceramic femoral head mounted to a stem extending into themedullary canal of the proximal femur to replace the femoral head. Jointreplacement surgery has become a proven and efficacious method ofalleviating pain and restoring function of the joint.

Current methods of preparing the rigid elements of a joint to receivecomponents as in joint replacement surgery involve extensive surgicalexposure. The exposure must be sufficient to permit the introduction ofdrills, reamers, broaches and other instruments for cutting or removingcartilage and bone that subsequently is replaced with artificialsurfaces. For total hip replacement, the acetabular articular surfaceand subchondral bone is removed by spherical reamers, the femoral headis resected with an oscillating saw, and the proximal medullary canal isshaped with broaches. A difficulty with total hip replacement is thatthe invasiveness of the procedure causes significant interoperativeblood loss and extensive rehabilitation because muscles and tendons mustbe released from the proximal femur to mobilize the femur and gainexposure of and access to the acetabular fossa.

Invasiveness. Conventional total hip arthroplasty is indicated forpainful arthritis of the hip joint. The procedure involves exposing thehip joint through a large incision to provide the surgeon fullvisualization of the hip joint and the acetabular region and to provideaccess for surgical power instruments. In order to appropriately preparethe bony structures of the hip joint, the major muscles spanning thejoint are commonly disrupted to gain adequate exposure of the joint.Steps of the procedure include removing the femoral head followed byreaming and broaching the proximal femoral canal to prepare a bonysurface to support a hip stem. The stem is implanted and may be cementedin place, or press fit for bony ingrowth. The acetabulum is typicallyprepared using a hemispherical reamer to remove cartilage down tobleeding bone. Once the acetabulum is prepared, an acetabular componentis implanted, either by cementing in place or press fitting for bonyingrowth. Surgical exposure is necessary to accommodate the bulk andgeometry of the components as well as the instruments for bonepreparation. The surgical exposure, which may be between six and twelveinches in length, may result in extensive trauma to the soft tissuessurrounding the hip joint along with the release of muscles that insertinto the proximal femur. The surgical exposure increases bleeding, pain,and muscle inhibition; all of which contribute to a longerhospitalization and rehabilitation before the patient can be safelydischarged to home or to an intermediate care facility.

The prepared bony surfaces are technically referred to as the acetabularfossa, femoral canal and metaphyseal region of the femur. Prior toplacing the final implants into the prepared spaces, a femoral trial,which may be the broach in some systems, is placed in the proximal femuralong with a trial femoral head and neck, and an acetabular trial isplaced into the acetabulum to facilitate trial range of motion andevaluation of hip stability prior to placement of the final total hipimplants.

For patients who require hip replacement it is desirable to providesurgical methods and apparatuses that may be employed to gain surgicalaccess to articulating joint surfaces, to appropriately prepare the bonystructures, to provide artificial, e.g., metal or plastic, articularbearing surfaces, and to close the surgical site, all withoutsubstantial damage or trauma to associated muscles, ligaments ortendons. To attain this goal, a system and method is needed to enablearticulating surfaces of the joints to be appropriately sculpted usingminimally invasive apparatuses and procedures.

A system to enable minimally invasive total hip arthroplasty that willminimize soft tissue trauma and accelerate postoperative rehabilitationis needed. Further, because minimally invasive techniques inherentlylimit observation of the surgical site, compromising visualization ofthe prepared bony surfaces, a device is also needed for inspection ofthe prepared bony surfaces. During a surgical procedure, bone debris andblood will gather in the surgical site and require removal from time totime to visualize the acetabulum. After preparation of the acetabulum,an acetabular component is implanted. A variety of acetabular componentssuch as cemented UHMWPE cups, cemented or press fit metal shells withUHMWPE, metal, or ceramic bearing liners are presently used. Typically,placement of a press fit shell requires an impaction force to fully seatthe implant into support bone. However, the size and location of theminimally invasive incision may not be optimal for proper orientationand application of force to adequately seat and stabilize an acetabularimplant. Thus, an impaction device is needed that allows for impactionof the acetabular component with the hip reduced or articulated for usewith a minimally invasive exposure for total hip arthroplasty. It mayalso be desirable to use a surgical navigation system to position theacetabular implant.

SUMMARY OF THE INVENTION

The present invention provides a system and method for total jointreplacement that involves minimally invasive surgical procedures. Theinstruments disclosed accomplish accurate bone preparation, implantorientation and implant fixation through a limited surgical exposure.

Thus, in one embodiment, the present invention provides a method ofappropriately sculpting the articular surface of a second bone thatnormally articulates with a first bone. The method involves attaching abone sculpting tool directly or indirectly to the first bone with thetool in bone sculpting engagement with the articular surface of thesecond bone, and then sculpting the articular surface of the second bonewith the joint reduced and moving one bone with respect to the other.Optionally, the bone sculpting tool may be attached to a mount that isattached directly or indirectly to the first bone. In some situations,it may be desirable to distract the second bone from the first boneduring surgery.

In a further embodiment, the invention provides a method ofappropriately preparing the articular surface of a second bone thatnormally articulates with a first bone and implanting a prostheticdevice. The method involves attaching a bone sculpting tool directly orindirectly to the first bone with the tool in bone sculpting engagementwith the articular surface of the second bone, and then sculpting thearticular surface by articulating one of the bones with respect to theother while bone preparation is performed. The bone sculpting tool maybe attached to a bone mount that is directly or indirectly attached toor integral with a stem, trial, reamer or broach implanted in themedullary canal of a bone.

Specifically, for example, the invention may be used for replacing thesurfaces of a femur and acetabulum through a minimal incision and withminimal disruption of musculotendinous structures about the hip. Atypical incision for a minimally invasive total hip procedure is betweentwo and four inches in length. It is noted that there may be somevariation in incision length due to patient physiology, surgeonpreferences, and/or other factors; the stated range is illustrative, notlimiting. In addition to a small incision, care is taken to approach thejoint capsule by separating tissues between muscle groups, rather thansectioning specific muscles. The invention includes; in variousembodiments:

1. A Minimally Invasive Acetabular Reamer System (MIAR)

The MIAR is either a modular or non-modular construct that, for hipapplications, comprises a femoral trial, a drive mechanism (eitherintegral or separate) and a hemispherical reamer or similar device forremoving cartilage and bone from the acetabular fossa. The reamingsystem enables placement of the components through a small incision andminimizes the number of components in the instrument set.

2. A Device to Illuminate and Visualize the Acetabulum

A fiber optic system is provided including a light source, fiber opticcable, imaging base and an imaging device and monitoring system toensure proper preparation of the acetabulum.

3. An Apparatus to Flush and Remove Bone Debris and Blood from theSurgical Site

An irrigation system and a suction system are provided. The irrigationand suction systems may be integral to the imaging base, or separateinstruments available for use as needed during the procedure.

4. A Minimally Invasive Acetabular Impaction System (MIAI)

An acetabular component, such as a press fit shell, is implantedfollowing preparation of the acetabulum. An impaction device is providedthat allows for impaction of the acetabular component with the hipreduced or articulated in order to fully seat a press fit acetabularcomponent into support bone of the acetabulum. The MIAI may not beneeded with some acetabular components. A surgical navigation system forpositioning the acetabular component may be used with the MIAI.

In the minimally invasive procedure, the hip is accessed through anincision adequate to expose the trochanteric fossa and allow resectionof the femoral neck and removal of the femoral head and neck segment.The femoral canal is accessed through the trochanteric fossa andtrochanteric region. Reamers, rasps and other devices as are known tothose skilled in the art are used to prepare the proximal femur toreceive a femoral implant by a sequence of reaming and broaching steps.Once prepared, the intramedullary canal and retained area of the femoralneck and trochanteric region are used to support the MIAR system toprepare the acetabulum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of hip anatomy and conventional exposure fortotal hip replacement;

FIG. 2 is an illustration of exposure for minimally invasive total hipreplacement with reamer;

FIG. 3 is an illustration of a minimally invasive acetabular reamer inaccordance with one embodiment of the present invention;

FIG. 4 is a cross sectional view of a minimally invasive acetabularreamer in a sagittal plane in accordance with one embodiment of thepresent invention;

FIG. 5 is a cross sectional view of a minimally invasive acetabularreamer cross in a transverse plane in accordance with one embodiment ofthe present invention;

FIG. 6 is an illustration of a minimally invasive acetabular reamer withan integral hydraulic drive in accordance with a further embodiment ofthe present invention;

FIG. 7 is an illustration of a minimally invasive acetabular reamer witha worm gear drive mechanism in accordance with yet another embodiment ofthe present invention;

FIG. 8 is an expanded view of a minimally invasive acetabular reamer inaccordance with one embodiment of the present invention;

FIG. 9 is an illustration of illumination, visualization, irrigation andsuction of an operative site in accordance with one aspect of thepresent invention;

FIG. 10 is an illustration of a minimally invasive impaction system inaccordance with one embodiment of the present invention; and

FIG. 11 is a detailed depiction of a minimally invasive impactor inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates the general anatomy of the hip joint and a typicalsurgical approach 10 to the hip joint to expose the proximal femur 11and the acetabulum 12. In traditional total hip replacement there aregenerally four surgical approaches to the hip joint. These includeposterior approaches without trochanteric osteotomy, trans-trochantericapproaches, anterior approaches without trochanteric osteotomy, andSmith-Peterson approaches. Such approaches are described in detail invarious orthopedic reference text such as “Operative Orthopedics,”edited by M. W. Chapman, MD, J. B. Lippincott Company, 1988. Inaddition, a direct lateral approach is commonly used for total hiparthroplasty. The most common surgical approach to the hip is posterior,and the musculature disrupted may include the short internal andexternal rotators, tensor fascia femoris, quadratus femoris, piriformis,and on occasion part of the gluteus medius and minimus, and the gluteusmaximus.

In minimally invasive total hip surgery, the incision 20 is typically 6cm as shown in FIG. 2. While 6 cm, or 2-4 inches, is a typical lengthfor a minimally invasive surgical incision, there may be some variationdue to patient physiology, surgeon preferences, and/or other factors.The surgical approach involves separating the gluteus maximus musclethrough blunt dissection to gain access to the hip joint capsule and thetrochanteric fossa. Muscle disruption is usually limited to release ofthe piriformis tendon at the trochanteric fossa. It should be noted thatthere are variations to the surgical approaches described that are knownto someone skilled in the art.

FIG. 2 illustrates a minimally invasive surgical approach to the hipjoint. The general approach is posterior, and the musculature disruptedincludes release of the piriformis tendon. The incision is just largeenough to expose the femoral head and acetabulum, and to enableplacement of a hemispherical reamer 22, drive mechanism 24, and femoralbroach 26.

In contrast to the minimally invasive technique provided, a total hipreplacement surgery involves exposing the hip joint through a largeincision to provide the surgeon full visualization of the hip joint andthe acetabular region and access for surgical power instruments. Thefemoral head is removed and the femoral canal is reamed and broached toprepare a bony surface to support a hip stem. The stem may be cementedin place, or press fit for bony ingrowth. The acetabulum is prepared,most typically using a hemispherical reamer attached to a surgical handdrill to remove cartilage down to bleeding bone. The surgical exposureas shown in FIG. 1 generally ranges between eight and twelve inches inlength and may result in extensive trauma to the soft tissuessurrounding the hip joint.

Minimally Invasive Acetabular Reamer System

As seen in FIG. 3, the MIAR of the present invention, for use with hipreplacement surgery, is either a modular or non-modular constructcomprising a femoral trial 32, a drive mechanism 33 (either integral orseparate) and a hemispherical reamer 34 or similar device for removingcartilage and bone from the acetabular fossa. The hemispherical reamer34 or similar device includes an attachment component (not shown) forattaching either to the femur, directly or indirectly, or to a mountthat itself is attachable to the femur, directly or indirectly.Discussion of the attachment of the MIAR to the femur, directly orindirectly, should be read as broadly encompassing attachment by thereamer directly to the femur (or femoral component) or attachment by thereamer to a mount that is attached to the femur (or femoral component).The reaming system, especially as a modular construct, enables placementof the components through a small incision and minimizes the number ofcomponents in the instrument set. In the minimally invasive procedure,the proximal femur does not have to be displaced during acetabularpreparation as is necessary with conventional hip arthroplasty.Therefore, the procedure requires only a minimal release of muscles andtendons and, consequently, minimal trauma to muscles and tendons thatattach to the proximal femur. Although the invention is described in thecontext of a total hip replacement, it is understood that the inventionhas application throughout orthopedics where the surfaces of anarticulating joint are to be modified or resurfaced to restore functionand relieve pain. The MIAR system uses a drive mechanism anchored to ormounted on a device such as a reamer, broach, or other suitable devicethat is secured to one bone and, with the joint reduced or placed inposition of reduction, may be activated to prepare, with a hemisphericalreamer, or suitable bone sculpting tool, the opposite side of the jointto receive artificial components.

With reference to the hip joint, the femoral head is removed eitherbefore or after the femoral canal is reamed and broached to prepare abony surface to support the hip stem or broach to be inserted. Theminimally invasive acetabular reamer is mounted to the broach, reamer,trial femoral component or other device inserted into the proximalfemur. It is possible to attach the MIAR directly to the proximal femur,however the instruments and the femoral implant provide an advantageoussupport structure as these instruments, such as rasps, broaches ortrials, or the implant conform closely to the prepared bony surface andprovides a rigid metal structure to which the MIAR may be mounted.Therefore, in the preferred embodiment, the MIAR is directly orindirectly attached to the femoral broach that is secured within theproximal femoral canal. It is noted that throughout the descriptionrasps, trials, broaches, implants, and stems are used interchangeably inrelation to the MIAR system. Additional embodiments include attachmentof the MIAR directly to the femur, the femoral trial or the femoralimplant. With the MIAR directly or indirectly attached to the femur, thereamer head is placed into the acetabulum. The MIAR is activated toinitiate cartilage and bone removal as the femur is positioned. Theoperating surgeon controls the MIAR by placing and/or moving the leg asnecessary to create a spherical reaming of the acetabulum.

The femoral trials are available in an array of sizes to accommodate thesize range of the proximal femur. The hemispherical reamers areavailable in a range of diameters to accommodate the size range of theacetabulum. In the preferred embodiment, the drive mechanism isinterchangeable amongst the femoral trails and amongst the hemisphericalreamers. An alternate embodiment includes a drive mechanism for eachfemoral trial, or groups of trials. The trials may be grouped by size,or by right and left. The example given is for the MIAR attacheddirectly or indirectly to a femoral rasp. Similar combinations arepossible when the drive mechanism is directly or indirectly attached toa femoral trial or femoral implant.

An example procedure according to the present invention includes thefollowing steps: the appropriate femoral trial is placed into theprepared proximal femur; the drive mechanism is placed onto the proximalaspect of the femoral trial followed by placement of the appropriatesized hemispherical reamer onto the drive mechanism; the hip is reducedand the reaming system is activated to prepare the acetabulum. Ofcourse, if the MIAR is not modular, it is placed as a unit, the hip isreduced, and the reaming system is activated.

As shown in FIG. 8, the acetabular reamer 34, which is provided in arange of sizes, attaches to the drive mechanism 33 at the support plate39 that provides quick attachment to the drive mechanism 33. The reameris preferably rigidly supported on the femoral side such that sufficientstability is provided to prevent relative motion between the MIAR andthe femur during articulation. Such stability is generally providedthrough the placement of the broach 32, femoral trial or femoral implantin the femoral canal. FIG. 3 illustrates an embodiment of a MIAR inaccordance with the present invention.

Support for the MIAR is provided by a femoral broach 32. The drivemechanism 33 is supported by the femoral broach 32. FIG. 3 further showsthe drive shaft 44 of the drive mechanism 33 supported in the drivemechanism housing, which is supported by the femoral broach 32.

As shown in FIG. 5, the drive mechanism 33 may use a worm 42 and wormgear 40 combination, bevel gears, spur gears, belts or chain drives, orother suitable mechanism to transfer rotation or oscillation to theacetabular reamer. In FIG. 4, a worm gear 40 is attached to the driveshaft 38 and in turn is driven by worm (behind worm gear). A worm andworm gear combination represents only one possible drive mechanism thatmay be used to drive the acetabular reamer and is intended to beillustrative but not limiting. Any other drive mechanism known to thoseskilled in the art may be used with the present invention. FIG. 5depicts the worm 42 supported by an input drive shaft 44.

As shown in FIG. 7, a flexible drive cable 31 is attached to the driveshaft 44. Optionally, a sleeve mounted to the drive mechanism housingmay extend through the surgical incision and contain the drive shaft 44and the flexible cable 31 is attached outside of the surgical incision.Torque generated by the drive mechanism is reacted between the drivemechanism and the femoral trial by a rotational stop 46.

The acetabulum is prepared by rotating or oscillating a hemisphericalreamer within the acetabulum. Alternatively, non-mechanical cuttinginstruments such as lasers, water jet cutting, ultrasonic probes,chemical, or other devices to remove tissue can be used. In the currentinvention, such devices involve rotation or oscillation of the reamerwith the device supported by the femur. As shown in FIG. 6, the MIAR maybe self-contained with an internal power source to drive the reamer, ormay have an external power source to drive the reamer. Likewise, themotor 35 may be internal to the drive mechanism, or may be external withtorque transferred to the drive mechanism via appropriate shaft orconnection. The drive mechanism may be constructed of mechanicalcomponents such as gears, cams, levers, belt and pulleys or chains. Thepower source may be electrical to drive an electrical motor, fluid todrive a hydraulic motor, gas to drive a pneumatic motor, or any othersuitable power source.

Alternatively, the drive mechanism may be configured for use with anyone of the attachment mechanisms provided by various manufacturers oftotal hip systems to attach trial necks to femoral trials. Theattachment thus may be a peg in groove, peg in hole, conical taper, ascrew fit, or threaded attachment. In a preferred embodiment, the drivemechanism is designed to attach to a femoral trial or rasp/trialprovided with the total hip system with which the MIAR is being used.The proximal surface of the drive mechanism is designed with a quickattach mechanism that fits an array of acetabular reamer sizes.

In another embodiment the drive mechanism is supported by the femoraltaper that supports the femoral head implant or implant trial. Thefemoral stem trial is placed into the prepared femoral canal and theappropriate femoral neck trial is placed onto the stem trial. The drivemechanism is placed onto the femoral neck trial taper and theappropriate sized acetabular reamer is directly or indirectly attachedto the drive mechanism. Optionally, the femoral stem trial and femoralneck trial may be integrally formed. In this approach, the femoral canalis prepared and the appropriate sized femoral stem is selected based onthe patient's femoral anatomy. The femoral stem implant is placed intothe prepared femur and the drive mechanism with appropriate sizedacetabular reamers is placed onto the implant to prepare the acetabulum.

In alternate embodiments, the drive mechanism may be integral to thefemoral trial or the acetabular reamers. The hemispherical reamers aremodular and allow changing reamer sizes during the procedure. As seen inFIG. 6, in surgical use, the appropriate femoral broach 32 with integraldrive mechanism, in this case a hydraulic motor 35, is placed into theproximal femur and the appropriately sized hemispherical reamer 34 isdirectly or indirectly attached to the drive mechanism. Alternatively,as seen in FIG. 7, the appropriate acetabular reamer 34 with integraldrive mechanism 33 is placed into the acetabular fossa 15 and directlyor indirectly attached to the femoral trail 32. Acetabular preparationis performed with the hip joint articulated (reduced).

FIGS. 3, 4, 5, 7 and 8 illustrate the mechanical drive mechanism used inone embodiment of the MIAR system. FIG. 7 shows the MIAR placed into theproximal femur 13 with the hemispherical reamer 34 in contact with theacetabulum 15. FIG. 8 illustrates an exploded view of one embodiment ofthe MIAR system. The drive shaft 38 extending distally from the drivemechanism 33 passes into receiving hole 82 to attach the drive mechanism33 to the broach 32. The anti-rotation pin 46 engages receiving hole 84to add stability and rotational resistance between the drive mechanismand broach. The reamer 34 attaches to a support platform 35 that is partof the drive mechanism 33. The surface 86 of the reamer 34 conicallylocks to the support platform 35.

FIG. 6 illustrates the MIAR with an internal drive mechanism. A trialbroach 32 is placed into the prepared proximal femur 13. The trial stemincludes a drive mechanism 35 that is housed within the proximal aspectof the broach 32. The drive mechanism 35, which may be a hydraulicmotor, within the broach rotates the drive shaft 37 and support plate 39which in turn rotates the acetabular 34 reamer to prepare theacetabulum. The acetabular reamer 34 is directly or indirectly attachedto the broach via the drive mechanism. Power sources for the drivemechanism to drive the reamer include hydraulic, pneumatic, electricmotor (either integral to the femoral trial or via flexible drive cableconnecting the motor to the drive mechanism), solenoid or other suitablepower source to provide rotation or oscillation to the reamer.Alternately, the drive mechanism may be driven by available surgicalpower instruments, such as surgical drills, Midas Rex and Anspaq hispeed drill/cutters, etc. Such equipment is available in pneumatic andbattery-operated forms. In a preferred embodiment, the drive mechanismis driven by an external power source transferring torque through aflexible drive shaft. Alternatively, the power source may be housedwithin the femoral trial or broach. The hemispherical acetabular reamersmay be reamers, cutters, or other device used for removing cartilage andbone from the acetabular fossa.

In yet another embodiment the acetabular reamer is assembled in acollapsed state to allow ease of reduction of the hip joint with theMIAR system in place. The acetabular reamer is elongated from thefemoral housing or from the drive or gear mechanism of the MIAR. Thiselongation may be accomplished by a variety of devices, for example shimplates, spacers, or other suitable device placed between the elements.Alternatively the MIAR may be elongated by means of pneumatic pressure,lead screw or other power sources. The manner by which the MIAR iselongated is not critical to the invention and any suitable device ormethod may be used. When sufficient resistance is encountered by thejoint capsule and/or other soft tissue elements about the hip, the MIARis activated to initiate acetabular bone preparation. The process ofacetabular reaming is enhanced by pressure created through tensioningthe soft tissue elements. In the example of using pneumatic force, gaspressure first elongates the MIAR construct and, after a specifiedamount of resistance is encountered to elongation, and pneumaticpressure is transferred to elements that generate torque to turn theacetabular reamer.

While minimally invasive techniques are advantageous from a patientrehabilitation perspective, they inherently limit observation of thesurgical site. Visualization of the prepared bony surfaces iscompromised by the limited access. As seen in FIG. 9, a fiber opticsystem is provided for inspection of the prepared bony surfaces. Thefiber optic system includes a light source (not shown), fiber opticcable 52, imaging base 50 and a digital camera, or other suitableimaging device, and monitoring system to ensure proper preparation ofthe acetabulum.

Additionally, during a surgical procedure, bone debris and blood willgather in the surgical site and may require periodic removal to enablevisualization of the acetabulum. Therefore, an irrigation system and asuction system are provided. Irrigation channels 56 pass through theimaging base 50 and are directed towards the acetabulum. The irrigationand suction systems may be configured as integral to the imaging base50, or provided as separate instruments available as needed during theprocedure.

In practice, the surgeon may periodically stop the reamer anddisarticulate the hip joint to view the preparation of the acetabulum.In a preferred embodiment, the imaging base is directly or indirectlyattached to the femoral trial, along with the irrigation and suctionsystems, after the hemispherical reamer and drive mechanism are removed.The imaging base is placed in proximity to the acetabulum byrepositioning the femur. The irrigation and suction systems may be usedto clear the site of bone debris and blood. The site is illuminated viathe fiber optic cable and light source. The digital camera, or otherimaging device, images the prepared acetabulum via the fiber optic cableand displays the image on the monitor. Alternatively, if the irrigationand suction systems are separate devices, they are used to clear thesite after the imaging base has been placed in proximity to theacetabulum.

Optionally, as seen in FIG. 9, the imaging base may be integral to thebase used to house the MIAR. The visualization may be done duringacetabular preparation and the imaging base need not be changed for theMIAR femoral part for visualization.

In combination with the imaging and irrigation system, and with theMIAR, a device to apply slight positive pressure to the surgical sitemay be beneficial in controlling blood loss. Pressure may be generatedby creating a sealed space over the incision, then applying a positivepressure within the surgical site.

Minimally Invasive Acetabular Impaction System

Once the acetabulum has been prepared, an acetabular implant is securedto the supporting bone, usually by either bone cement or press-fit. Inthe case of a cemented acetabular component, the bone surface isoversized relative to the implant size. The bony surface and the implantare covered with bone cement. The implant is then placed into theacetabulum and pressed into position forming a uniform layer of bonecement between the acetabular component and supporting bone. In the caseof a press fit acetabular component, the bone surface is line-to-line orslightly undersized relative to the implant size. The implant isimpacted into place in the supporting bone. In standard total hipsurgery, a straight handled impactor is commonly used to impact theacetabular component. The extensive exposure typically used intraditional total hip surgery provides the clearance to align theimpactor relative to the acetabulum. However, in the case of a minimallyinvasive total hip, the incision is too small to allow properorientation of a standard straight handled impactor. Use of a standardimpactor requires making a second incision to pass the impactor throughmuscle and tissue in the correct orientation relative to the acetabulum.The acetabular component must be positioned properly to provide normalfunction and to prevent dislocation of the hip joint. Making a secondincision and disrupting more muscle is contrary to the goal of aminimally invasive procedure. Therefore, a device that impacts theacetabular component through a minimally invasive incision is needed. Inone embodiment, the current invention includes a device designed todirectly or indirectly attach to the femoral trial and provide animpaction force to properly seat the implant. A variety of acetabularcomponents and methods for placement thereof may be used. Examplecomponents for implanting in the acetabulum include, but are not limitedto, cemented shells or press fit cups.

As seen in FIG. 10, the impaction device preferably includes a pneumaticimpaction hammer 102 mountable to the femoral broach 32 and an optionalattachment component for attaching to the shell 60 of the acetabularcomponent. The impaction device 102 and acetabular component 60 may beplaced into the surgical site independently and assembled in theoperative site. Alternatively, the impaction device 102 and acetabularcomponent 60 may be assembled prior to placing the impaction device ontothe broach 32. With the acetabular shell directly or indirectly attachedto the impactor, and the impactor secured to the femoral broach, theshell is placed into the acetabulum by reducing the hip joint. Thebroach, femur and mass of the leg serve as counter weights to counteractthe force of the impaction device. An additional counter weight may bedirectly or indirectly attached to the impaction device via a connectionshaft extending out of the incision and attaching to a weight orexternal resistance to impaction forces.

The impaction device may be powered by a pneumatic impaction hammer, ahydraulic piston, a linear actuator or solenoid, an electromechanicaldevice, a spring activated device, or any other suitable forcegenerating mechanism. The power source may originate outside of theoperative site, or may be integral with the impaction device. As analternative a hand held impactor with a handle angled to allow accessthrough a minimally invasive incision may be used to impact theacetabular component. In a preferred embodiment, the impactor is asingle ended air driven piston and cylinder as show in FIG. 11. The backface 123 of the impactor housing 111 is configured to attach to thebroach previously described. Within the housing is a primary piston 118that travels in a primary cylinder 124. In its retracted position(shown) a push rod 120 of a secondary piston 117 engages a retaininggroove 121 in a primary piston 118. The secondary piston 117 is held inan extended position by a secondary spring 116. Air pressure is appliedvia a primary tube 119 to the back of the primary piston 118 to chargesystem. The primary piston 118 is held in place by the push rod 120 ofthe secondary piston 117. Air pressure is applied to the secondary tube115 to pull the push rod and the secondary piston 117 out of theretaining groove 121 in the primary piston 118, thereby releasing theprimary piston 118 to impact the top surface of the cylinder 126. Theimpaction force is carried through the impactor housing 111 anddelivered to the acetabular shell (not shown) via a cup adaptor 110. Thecup adaptor 110 has a threaded end 122 that engages the acetabularshell. The other end of the cup adaptor 110 has a box shaped recess 127that fits over a mating prominence 112 on the top surface of theimpactor housing 111.

After an impaction cycle the pressure to the primary tube 119 isreleased and the primary piston 118 is forced back into a retractedposition by a return spring 114. When the primary piston 118 is in itsretracted position the air pressure to the secondary tube 115 isreleased and the secondary piston 117 is pushed back into lockedposition by a secondary return spring 116. Pressure is reapplied to theprimary tube 119 to charge the impactor and the cycle is repeated.

In surgical use, the cup impactor 102 and broach may be assembledoutside of the surgical site, then placed into the prepared proximalfemur. Alternatively, the broach may first be placed into the proximalfemur, then the cup impactor 102 attached to the broach. With the cupimpactor 102 in place, the cup adaptor 110 is attached to the cupimplant and the recess 127 in the adapter is placed over the matingprominence 112 on the top of the cup impactor. The hip joint is reduced,placing the acetabular shell into the acetabulum. An alignment guide(not shown) is attached to the cup impactor to aid the surgeon inproperly orientating the shell with respect to the pelvis.Alternatively, a surgical navigation system may be used to position theacetabular shell by referencing the cup impactor and the acetabulum.Once in position, the shell is impacted into the acetabulum bytriggering the cup impactor with successive impactions. In a preferredembodiment the trigger releases one impaction, then the cup impactorresets for a further impaction, as necessary. In an alternate embodimentthe trigger releases continuous impactions for the duration the triggeris on.

Or course the impaction device is suitable for use in placing an implantother than an acetabular component. The impaction device may be used forseating an implant in a second bone in any joint replacement wherein theimplant may be placed on the impaction device, aligned with a secondbone, and force imparted to the implant, the force being reacted withthe first bone and the second bone.

A Typical Surgical Procedure for the MIAR is as Follows

Using the instrumentation shown, the articular surface of the acetabulummay be sculpted according to the patient's individual physiology byarticulating the femur with reference to the acetabulum. The methodinvolves providing an apparatus having a bone sculpting tool directly orindirectly attached to a bone mount, such as a femoral trial stem,attaching the mount rigidly to the femur with the tool in bone sculptingengagement with the acetabulum, and then sculpting the acetabulum byarticulating the femur with respect to the joint.

The hip joint is a ball in socket joint, hence rotation of the femurwhile supporting the MIAR will result in a spherical preparation of theacetabulum. Alternatively, the MIAR, having a suitable reamer and drivemechanism, may be placed into the acetabulum to remove bone withoutrotating the femur.

In a preferred embodiment, the trochanteric fossa is surgically accessedwith a minimal disruption of muscle and tendon insertions to thetrochanter and surrounding area. The approach may be at the posteriorborder of the gluteus medius and minimus, anterior in the intervalbetween sartorius and rectus, or a direct lateral exposure. The hip maybe dislocated posteriorly if a posterior approach is used or anteriorlyif either a lateral or anterior approach is used. Alternatively, the hipmay remain reduced while the femoral canal is prepared and the femoralneck is resected.

The femoral neck is resected and the femoral head is removed. Theresection and removal may be performed with conventional cutting devicessuch as oscillating saws. The femur is oriented to align the femoralcanal with the incision. The femoral canal is prepared using sequentialreaming and broaching. Bony preparation is per the technique specifiedfor the particular total hip stem being used and at the surgeon'sdiscretion.

An appropriately sized femoral trial is placed into the femur. The drivemechanism is directly or indirectly attached to the femoral trial.Preferably, the drive mechanism is designed to mount directly onto thefemoral trial.

The acetabular reamer is directly or indirectly attached to the drivemechanism. The appropriate acetabular reamer is selected by the surgeon.The surgeon may choose to measure the diameter of the removed femoralhead as an aid in selecting the most appropriately sized acetabularreamer.

The hip joint is reduced and the hip is articulated with the drivemechanism and acetabular reamer in place. Elongation of the MIARconstruct is optionally carried out to appropriately tension the softtissue elements about the hip. The drive mechanism is activated toprepare the acetabulum. If necessary, the femur may be advanced whilethe hip joint is manipulated to ensure spherical and uniform reaming ofthe acetabulum. Imaging may be used to check the orientation and depthof the acetabular reamer.

At the surgeon's discretion, depth of reaming and uniformity of reamingmay be checked periodically during the procedure. This may be done bydislocating the hip, removing the reamer and attaching the illuminationand irrigation devices (or a combined illumination and irrigationdevice) to the femoral trial. The hip is reduced with the illuminationand irrigating devices in place and the operative site is cleared withirrigation and suction. The prepared surface of the acetabulum may thenbe inspected. After inspection, the illumination and irrigation devicesare removed and the drive mechanism and reamer are replaced.Alternatively, depth of reaming may be assessed under fluoroscopicimaging of the hip joint.

The articulation of the hip joint to prepare the acetabulum may berepeated with sequentially larger reamers until the appropriate size isreached. Further, the size and preparation may be checked with theillumination and irrigation devices as necessary. Once the appropriatesize is reached, the acetabular reamer and the drive mechanism areremoved.

After preparation of the acetabulum, an appropriate acetabular componentis implanted. The appropriate acetabular component may be pre-selectedor may be selected after surgical preparation of the acetabulum. If thedesired component is a cemented cup, the cup is cemented in place.

If the desired component is a press fit cup, a cup impactor is attachedto the broach and placed into the prepared proximal femur.Alternatively, the broach may be place in the prepared femoral canalfirst and then attach the cup impactor to the broach. The acetabularshell is attached to the cup adaptor and placed onto cup impactor. Thehip joint is reduced and the shell is positioned in the acetabularfossa. An alignment guide is attached to the cup impactor to aid thesurgeon in proper orientation of the shell during impaction. The cupimpactor is triggered, thereby impacting the shell. An alternativetechnique for placing a press fit cup may use image guided surgery or analignment device protruding from the incision. The guiding system isused to advance the cup into proper orientation. The MIAI impactor isactivated to securely seat the cup into the acetabulum. Regardless oftechnique, after placement of the press fit cup, the impaction device isremoved. Alternatively, a surgical navigation system may be used forpositioning, aligning, and monitoring the cup or cup impactor duringimpaction. Cup monitoring includes real time evaluation of the cupposition relative to anatomical landmarks captured by the surgicalnavigation system after preparing the acetabulum and before placing thecup so as to indicate cup seating and cup alignment.

The acetabular liner is placed into the shell and a trial femoral neckand head are placed onto the femoral trial. The range of motion and hipstability are checked and the appropriate femoral implant is selected.The femoral trials are removed and the femoral component is implantedper manufacturer specifications.

Additional steps as known to those skilled in the art may be performedwithin the scope of the invention. Further, one or more of the listedsteps need not be performed in a procedure within the scope of thepresent invention.

What is claimed is:
 1. An apparatus for sculpting the articular surfaceof a second bone that normally articulates with a first bone, theapparatus comprising: a bone sculpting tool including an attachmentportion for attaching the bone sculpting tool to the first bone in aposition for sculpting the articular surface of the second bone.
 2. Theapparatus of claim 1, further comprising a mount for attachment to theattachment portion, the mount being adapted for attachment to the femur.3. The apparatus of claim 1, wherein the bone sculpting tool isconfigured for attachment to a femur in a position for sculpting thearticular surface of an acetabulum.
 4. The apparatus of claim 3, whereinthe attachment portion is adapted for direct attachment to the femur. 5.The apparatus of claim 3, wherein the attachment portion is adapted forindirect attachment to the femur.
 6. The apparatus of claim 5, whereinthe attachment portion is adapted for attachment to a femoral trial. 7.The apparatus of claim 5, wherein the attachment portion is adapted forattachment to a femoral broach.
 8. The apparatus of claim 5, wherein theattachment portion is adapted for attachment to a femoral stem.
 9. Theapparatus of claim 3, wherein the bone sculpting tool is designed forrotation.
 10. The apparatus of claim 3, wherein the bone sculpting toolis designed for oscillation.
 11. The apparatus of claim 3, wherein thebone sculpting tool comprises a hemispherical reamer.
 12. The apparatusof claim 3, further including a drive mechanism for driving the bonesculpting tool.
 13. The apparatus of claim 12, wherein the drivemechanism is integral to a mount.
 14. The apparatus of claim 12, whereinthe drive mechanism is integral to a femoral trial.
 15. The apparatus ofclaim 12, wherein the drive mechanism is configured for attachment to afemoral stem.
 16. The apparatus of claim 3, wherein the bone sculptingtool is adapted for elongation.
 17. The apparatus of claim 16, whereinthe bone sculpting tool has an axis of rotation, and the elongation isalong the axis of rotation.
 18. The apparatus of claim 16, furtherincluding a lead screw for elongation of the bone sculpting tool. 19.The apparatus of claim 16, further including shims for elongation of thebone sculpting tool.
 20. The apparatus of claim 16, further including apneumatic powered device for elongation of the bone sculpting tool. 21.The apparatus of claim 12, wherein the drive mechanism comprises agearbox.
 22. The apparatus of claim 12, wherein the drive mechanismcomprises a worm and worm gear combination.
 23. The apparatus of claim12, wherein the drive mechanism comprises a bevel gear combination. 24.The apparatus of claim 12, wherein the drive mechanism includes a motor.25. The apparatus of claim 12, further including a flexible drive shaftfor connecting the drive mechanism to a motor.
 26. The apparatus ofclaim 24, wherein the motor is a surgical power drill.
 27. A method ofsculpting the articular surface of a second bone that normallyarticulates with a first bone in a joint, the method comprising thesteps of: providing a bone sculpting tool; attaching the bone sculptingtool to the first bone in a position for sculpting the articular surfaceof the second bone; aligning the bone sculpting tool with the secondbone; and sculpting the articular surface of the second bone by engagingthe bone sculpting tool with the articular surface of the second bone.28. The method of claim 27, wherein the step of attaching the bonesculpting tool to the first bone includes attaching the bone sculptingtool to a mount and attaching the mount to the first bone.
 29. Themethod of claim 27, wherein the step of attaching the bone sculptingtool to the first bone includes attaching the bone sculpting tooldirectly to the first bone.
 30. The method of claim 27, wherein the stepof attaching the bone sculpting tool to the first bone includesattaching the bone sculpting tool indirectly to the first bone.
 31. Themethod of claim 27, wherein: the step of attaching the bone sculptingtool to the first bone comprises attaching the bone sculpting tool to afemur; the step of aligning the bone sculpting tool with the second bonecomprises placing the bone sculpting tool in the acetabulum; and thestep of sculpting the articular surface of the second bone by engagingthe articular surface of the second bone comprises sculpting thearticular surface of the acetabulum by engaging the articular surface ofthe acetabulum.
 32. The method of claim 31, wherein the step ofattaching the bone sculpting tool to the femur includes attaching thebone sculpting tool directly to the femur.
 33. The method of claim 31,wherein the step of attaching the bone sculpting tool to the femurincludes attaching the bone sculpting tool indirectly to the femur. 34.The method of claim 33, wherein the step of attaching the bone sculptingtool to the femur comprises the steps of attaching the bone sculptingtool to a femoral trial and placing the femoral trial in the femur. 35.The method of claim 33, wherein the step of attaching the bone sculptingtool to the femur comprises the steps of attaching the bone sculptingtool to a broach and placing the broach in the femur.
 36. The method ofclaim 33, wherein the step of attaching the bone sculpting tool to thefemur comprises the steps of attaching the bone sculpting tool to afemoral implant and implanting the femoral implant in the femur.
 37. Themethod of claim 31, further including the steps of elongating the bonesculpting tool to engage the acetabulum and tensioning soft tissuestructures spanning the joint.
 38. The method of claim 31, furtherincluding the step of retracting the bone sculpting tool to ease thestep of placing the bone sculpting tool within the acetabulum.
 39. Asystem for minimally invasive sculpting and replacing the articularsurface of a second bone that normally articulates with a first bone,the system comprising: a bone-sculpting apparatus comprising abone-sculpting tool including a tool attachment portion for attachingthe bone sculpting tool to the first bone in a position for sculptingthe articular surface of the second bone; and an impaction apparatus forproviding force between the first bone and the second bone, theimpaction apparatus comprising an impaction device including animpaction attachment portion for attaching the impaction device to thefirst bone.
 40. The system of claim 39, wherein the impaction apparatusfurther comprises an adapter for mounting the implant.
 41. The system ofclaim 39, wherein further including a visualization apparatus,irrigation apparatus, and a suction apparatus all configured as a singledevice.
 42. The system of claim 39, further comprising a visualizationapparatus comprising a light source, an imaging base, an imaging device,and a display.
 43. The system of claim 41, wherein the visualizationapparatus further includes a monitoring system.
 44. The system of claim42, wherein the imaging base is integral to a mount configured forattachment to the attachment portion of the bone sculpting apparatus,the mount being attachable to the first bone.
 45. The system of claim42, further including an irrigation apparatus integral to the imagingbase.
 46. The system of claim 42, further including a suction apparatusintegral to the imaging base.
 47. The system of claim 42, furtherincluding an irrigation apparatus and a suction apparatus integral tothe imaging base.
 48. The system of claim 39, further including anirrigation apparatus.
 49. The system of claim 39, further including asuction apparatus.
 50. The system of claim 39, further including asurgical navigation system for positioning, aligning and monitoring theimplant.
 51. The system of claim 39, further including a surgicalnavigation system for positioning, aligning and monitoring the impactiondevice.
 52. A method of sculpting, in a surgical site, the articularsurface of a second bone that normally articulates with a first bone,the method comprising the steps of: providing a bone sculpting tool;attaching the bone sculpting tool to the first bone; aligning the bonesculpting tool with the second bone and sculpting the articular surfaceof the second bone by engaging the bone sculpting tool with thearticular surface of the second bone; providing an implant; providing animpaction apparatus comprising an impaction device configured forattachment to the first bone; attaching the impaction apparatus to thefirst bone; placing the implant on the impaction apparatus and impartingforce to the implant to secure the implant to the second bone, the forcebeing reacted by the second bone and the first bone.
 53. The method ofclaim 52, further including a monitoring device including avisualization apparatus, an irrigation apparatus, and a suctionapparatus.
 54. The method of claim 52, further comprising the steps ofproviding a visualization apparatus comprising a light source, animaging base, an imaging device, and a display system and visualizingthe surgical site with the visualization apparatus.
 55. The method ofclaim 52, further comprising the steps of providing an irrigationapparatus and a suction apparatus and clearing the surgical site of bonedebris and blood using the irrigation apparatus and the suctionapparatus.
 56. The method of claim 52, further comprising the step ofclearing the site of bone debris and blood using the irrigationapparatus and the suction apparatus.
 57. The method of claim 52, furthercomprising the steps of positioning, aligning and monitoring the implantwith a surgical navigation system.
 58. The method of claim 52, furthercomprising the steps positioning, aligning and monitoring the impactiondevice with a surgical navigation system.
 59. The method of claim 52,wherein: the step of attaching the bone sculpting tool to the first bonecomprises attaching the bone sculpting tool to a femur; the step ofaligning the bone sculpting tool with the second bone and sculpting thearticular surface of the second bone comprises placing the bonesculpting tool within an acetabulum and sculpting articular surface ofthe acetabulum; the step of attaching the impaction apparatus mount tothe first bone comprises attaching the impaction apparatus mount to afemur; and the step of imparting force to the implant comprisesimparting force to an acetabular shell for securing the acetabular shellto the acetabulum, the force being reacted by the acetabulum and thefemur.